Metal matrix composites have excellent tensile strength and stiffness. Some Metal matrix composites (MMCs) are made by placing a porous ceramic preform into a mold cavity and infiltrating with aluminum. In order to assure that the mold will close, the preform dimensions, including tolerances, must be less than the mold cavity depth. Therefore, there will always be gaps between the preform and mold surfaces. These gaps will fill with aluminum and form aluminum rich layers at the surface. Where the surfaces of the MMC are aluminum rich the resulting metal matrix composite is not homogenous throughout its thickness.
Also, the location of the porous preform is not fixed within the mold cavity, so the aluminum rich surface layer may be different on one side than the other. In the worst case, the aluminum rich surface layer may be almost zero thickness on one side and thick on the other side. It is desired that the porous preform be held to the center of the cavity, so that the aluminum rich surface layers are equal thickness on both sides of the preform.
It is an object of the present invention to utilize a low volume fraction compressible ceramic fiber paper on the top and bottom layers of the preform used to make a Metal Matrix Composite (MMC) to ensure a consistent uniform layer of encapsulating aluminum without the need for exacting standards in preform dimensions.
It is a further object of the present invention to utilize a low volume fraction compressible ceramic fiber paper on the top and bottom layers of the preform used to make a Metal Matrix Composite (MMC) to exert an equal and balanced force on both sides of the preform to center the preform within the mold cavity prior to metal infiltration.